1. Field of the Invention
The present invention relates to a serial-to-parallel converter circuit and a liquid crystal display driving circuit.
2. Description of the Related Art
Recently, there has been mainly adopted a serial interface transferring serial data, as a data transfer system between a device at transmitting-side and a device at receiving-side. The examples therefor are a three-wire serial interface (serial data DI, a serial clock CL, a chip enable CE), a four-wire serial interface (serial data SI, serial data SO, a serial clock CL, a chip enable CE), a two-wire serial interface (serial data SDA, a serial clock SCL), etc. While data format to be used for transferring data from the device at transmitting-side to the device at receiving-side is serial data, data format to be used for processing in the device at receiving-side is parallel data. Therefore, a device at receiving-side employing a serial interface is required to provide a serial-to-parallel converter circuit (see, for example, Japanese Patent Laid-Open Patent Publication No. 2003-218705).
In a system including a device at transmitting-side and a device at receiving-side, there is a case where serial data of a new number of input bits needs to be dealt with for the purpose of achieving high functionality, etc. For example, in a LCD (Liquid Crystal Display) driving system, in which a device at transmitting-side is a microcomputer and a device at receiving-side is a LCD module for driving and displaying a LCD panel, there is a case where 8-bit display data (composed of segment signal, common signal and display control data, and hereinafter referred to as 8-bit serial data) needs to be deal with, in addition to original 6-bit display data (composed of segment signal, common signal and display control data, and hereinafter referred to as 6-bit serial data), for example.
However, a serial-to-parallel converter circuit originally provided in the LCD module (device at receiving-side) is a circuit intrinsically supporting original 6-bit serial data. For instance, a serial-to-parallel converter circuit supporting 6-bit serial data is usually configured with a shift register obtained by cascade-connecting six stages of flip-flops, and is not able to support serial data of other than 6 bits. Therefore, there is simply considered such an improvement that a serial-to-parallel converter circuit supporting 8-bit serial data and a signal processing system dealing with 8-bit parallel data are newly provided in the LCD module (device at receiving-side).
However, when making such an improvement to the LCD module (device at receiving-side), various improvements are also required of a microcomputer (device at transmitting-side) accordingly. To be more specific, an easily conceivable way is providing the LCD module (device at receiving-side) with a control input terminal for identifying 6-bit serial input data or 8-bit serial input data, which is transferred from the microcomputer (device at transmitting-side). In this case, on the microcomputer side (device at transmitting-side), a software is needed to be improved so as to set a transmission format (rules for data format, procedure of transmission, etc.) of a control signal to be input to the control input terminal (signal indicating that an input signal is either a six-bit signal or an eight-bit signal), etc. Furthermore, in accordance with such an improvement of the software, there may be needed an improvement for a hardware such that a control output terminal for outputting the control signal is added, etc.
As described above, the compatibility with existing devices at transmitting-side cannot be maintained only by making an improvement to devices at receiving side, just like an addition of a signal processing system such as a serial-to-parallel converter circuit supporting serial data of a new number of input bits. The compatibility means characteristics that a plurality of elements to be combined can be substituted with each other. Therefore, an improvement becomes necessary for existing devices at transmitting-side and, thereby causing a problem that the time of system development is extended and the cost thereof increases.